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Deuterium Isotopomers As a Tool in Environmental Research UMEÅ UNIVERSITY MEDICAL DISSERTATION New Series No. 1070 ISSN: 0346-6612 ISBN: 91-7264-218-1 Edited by the Dean of the Faculty of Medicine Deuterium isotopomers as a tool in environmental research by Tatiana Betson Department of Medical Biochemistry and Biophysics, Umeå University Umeå 2006 Department of Medical Biochemistry and Biophysics Umeå University SE-901 87 Umeå, Sweden Copyright © 2006 Tatiana Betson ISSN 0346-6612 New Series No. 1070 ISBN 91-7264-218-1 Printed in Sweden by Print and Media Umeå University, Umeå À ma famille passée, présente et future Table of contents Abbreviations 6 Abstract 7 Publication list 8 Introduction 9 Stable isotopes 11 General considerations 11 Definitions 12 Mechanisms of isotope fractionation 13 1) Physical fractionations 13 2) Chemical fractionations 14 Isotopomers 16 Measurements of isotope and isotopomer abundance 17 1) IRMS 17 3) FTIR 19 2) NMR 19 Climate change 23 Open questions 23 Tree rings as a proxy for climate (dendroclimatology) 24 1) Physical characteristics of tree rings 25 2) Chemical characteristics of tree rings 26 Persistent organic pollutants in the environment 29 Definition 29 Identification of their origin and fate 29 Results and conclusions 31 Paper I 31 Paper II 31 Paper III 32 Paper IV 33 Unpublished results related to Paper IV 33 General conclusion 35 Acknowledgements 36 References 38 5 Abbreviations D (or 2H) Deuterium p,p’-DDT p,p’-dichlorodiphenyltrichloroethane o.p’-DDD o.p’-dichlorodiphenyldichloroethane DID Deuterium Isotopomer Distribution FID Free Induction Decay FTIR Fourier Transform Infra Red spectroscopy 1H Protium (or proton) IRMS Isotope Ratio Mass Spectrometry KIE Kinetic Isotope Effect NMR Nuclear Magnetic Resonance spectroscopy PHC Polyhalogenated Compounds POP Persistent Organic Pollutants TMS Tetramethylsilane VPDB Vienna PeeDee Belemnite VSMOW Vienna Standard Mean Ocean Water 6 Abstract Deuterium isotopomers as a tool in environmental research This thesis describes the development and the use of quantitative deuterium Nuclear Magnetic Resonance spectroscopy (NMR) as a tool in two areas of environmental research: the study of long term climate-plant interactions and the source tracking of persistent organic pollutants. Long-term interactions between plants and climate will influence climate change during this century and beyond, but cannot be studied in manipulative experiments. We propose that long tree-ring series can serve as records for tracking such interactions during past centuries. The abundance of the stable hydrogen isotope deuterium (D) is influenced by physical and biochemical isotope fractionations. Because the overlapping effects of these fractionations are not understood, studies of the D abundance of tree rings led to conflicting results. We hypothesized that both types of fractionations can be separated if the D abundance of individual C-H groups of metabolites can be measured, that is if individual D isotopomers are quantified. The first paper describes a technique for quantification of D isotopomers in tree-ring cellulose by NMR. The technique showed that the D isotopomers distribution (DID) was non-random. Therefore, the abundance of each isotopomer potentially contains individual information which suggests an explanation for the conflicting results obtained by measuring the overall D abundance (δD). In the second paper, this technique was used to study hydrogen isotope exchange during cellulose synthesis in tree rings. This revealed that some C-H positions exchange strongly with xylem water, while others do not. This means that the exchanging C-H positions should acquire the D abundance of source water, which is determined by physical fractionations, while non-exchanging C-H positions of tree- ring cellulose should retain biochemical fractionations from the leaf level. Therefore, the abundance of the corresponding D isotopomers should contain information about climate and physiology. When analysing tree-ring series, the DIDs should reflect information about temperature, transpiration and regulation of photosynthesis. In the third paper, we showed that CO2 concentration during photosynthesis determines a specific abundance ratio of D isotopomers. This dependence was found in metabolites of annual plants, and in tree-ring cellulose. This result shows that D isotopomers of tree-ring series may be used to detect long-term CO2 fertilisation effects. This information is essential to forecast adaptations of plants to increasing CO2 concentrations on time scales of centuries. In the fourth paper, the source of persistent organic pollutants in the environment was tracked using DID measurements. The δD values of two compounds of related structures were not enough to show indisputably that they did not originate from the same source. However, the DIDs of the common part between the two compounds proved that they did not originate from the same source. These results underline the superior discriminatory power of DIDs, compared to δD measurements. The versatility of DID measurements makes them a precious tool in addressing questions that cannot be answered by δD measurements. Key words: Deuterium, NMR, isotopomers, CO2 response, climate reconstruction, persistent pollutants, stable isotopes. 7 Publication List This thesis is based on the following publications, which will be referred to in the text by their roman numerals: I - Quantification of deuterium isotopomers in tree-ring cellulose Tatiana R. Betson, Angela Augusti and Jürgen Schleucher, Analytical Chemistry, 2006, in press. II - Hydrogen exchange during cellulose synthesis distinguishes climatic and biochemical isotope fractionations in tree ring, Angela Augusti, Tatiana R. Betson and Jürgen Schleucher, New Phytologist, 2006, vol 172, issue 3, p 490-499. III – Deuterium Isotopomers record a CO2 response of plants in leaves and tree-rings Angela Augusti, Tatiana R. Betson and Jürgen Schleucher, Manuscript. IV - Baseline isotopic data of polyhalogenated compounds Walter Vetter, Wolfgang Armbruster, Tatiana R. Betson, Jürgen Schleucher, Thomas Kapp and Katja Lehnert, Analytica Chimica Acta, 2006, vol 577, issue 2, p 250-256. The papers have been reprinted with the kind permission of ACS publications (paper I), Blackwell Publishing (paper II), Elsevier (paper IV) © 2006 8 Introduction Most chemical elements of biochemical interest such as hydrogen, carbon, nitrogen and oxygen are composed of different stable isotopes. The abundances of the heavy stable isotopes (2H, also known as Deuterium (D), 13C, 15N, 17O and 18O) are much smaller compared to the light stable isotopes (1H, 12C, 14N and 16O) and are modified by physical and biochemical processes. One common use of heavy stable isotopes is to label compounds in a harmless way. This provides a non-invasive tool in medicine to diagnose metabolic disorders (Goetze et al., 2005) and to detect potential disease (Levine et al., 2004) and in medical studies to better understand human metabolism (Jin et al., 2004; Ribeiro et al., 2005). Stable isotopes are also widely used to track biogeochemical fluxes through the carbon and nitrogen cycles (Hobbie et al., 2002; Nasholm et al., 1998). In chemistry and biochemistry, labelling is also used in NMR structure determination (Wider & Wuthrich, 1999), to study reaction mechanisms (Ankianiec et al., 1994; Barta et al., 1994; Cook & Cleland, 1981) and to determine kinetic isotope effects (Cleland, 1980). Because their natural abundances are modified by physical and chemical fractionations, stable isotopes are also a precious tool at natural abundance. They are used to study enzyme mechanisms (Cleland, 2003), metabolic fluxes (Smith & Ziegler, 1990; Zhang et al., 1995; Zhang et al., 1994) and to determine kinetic isotope effects (Singleton & Thomas, 1995; Lee et al., 2004). In biogeosciences, stable isotopes at natural abundance are used to integrate biogeochemical fluxes from local to global scale. Prominent examples are the study of the carbon and nitrogen cycles within ecosystems (Ekblad & Hogberg, 2001; Hogberg, 1997) and quantification of sources and sinks of the greenhouse gases CO2, N2O and CH4 (Francey et al., 1995; Dore et al., 1998; Lowe et al., 1994; Quay et al., 1999). They are also an invaluable tool to reconstruct past climate from archives such as ice cores and tree rings (Petit et al., 1999; 9 Jouzel et al., 2006; Buhay & Edwards, 1995; Masson-Delmotte et al., 2005). Most of the measurements of stable isotope abundance are made using isotope ratio mass spectrometry (IRMS). This technique measures the ratio of heavy to light isotope of whole molecules. However, it has been shown for all heavy isotopes that their abundance in non-equivalent intramolecular positions is variable (Martin & Martin, 1981; Schmidt, 2003; Robins et al., 2003). Because a molecule carrying a heavy isotope in a particular position is called an isotopomer, this variation can be described by isotopomer distributions. These distributions contain information about the origin of compounds (Zhang et al., 2002). Isotopomer distributions have only been measured by IRMS in a few cases. To measure isotopomer distributions, nuclear magnetic resonance (NMR) is probably the most effective tool. Isotopomer analysis by NMR is used in food authentication (Martin et al., 1988; Remaud et al., 1997), biomechanisms (Zhang et al., 1995) and kinetic isotope effects studies (Lee et al., 2004). But isotopomer measurements are still uncommon compared to measurements of isotope ratios. However, limitations of isotope ratio measurements
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